U.S. patent application number 11/810025 was filed with the patent office on 2008-05-01 for droplet ejecting apparatus.
This patent application is currently assigned to Fuji Xerox Co., Ltd.. Invention is credited to Masami Furuya, Kenichi Kawauchi, Susumu Kibayashi.
Application Number | 20080100655 11/810025 |
Document ID | / |
Family ID | 39329583 |
Filed Date | 2008-05-01 |
United States Patent
Application |
20080100655 |
Kind Code |
A1 |
Furuya; Masami ; et
al. |
May 1, 2008 |
Droplet ejecting apparatus
Abstract
In a droplet ejecting apparatus, a detection pattern output unit
drives a droplet ejecting head based on a pulse signal and image
information of a detection pattern comprising plural unit patterns
so as to form an image of the detection pattern on a recording
medium. A correction information generating unit derives a distance
between adjacent unit patterns based on the image of a read
detection pattern, compares the distance with a distance according
to the conveyance velocity of the recording medium by a moving
unit, and generates correction information so as to enlarge the
pulse width when the derived distance is shorter, and to reduce the
pulse width when the derived distance is longer.
Inventors: |
Furuya; Masami; (Kanagawa,
JP) ; Kawauchi; Kenichi; (Kanagawa, JP) ;
Kibayashi; Susumu; (Kanagawa, JP) |
Correspondence
Address: |
FILDES & OUTLAND, P.C.
20916 MACK AVENUE, SUITE 2
GROSSE POINTE WOODS
MI
48236
US
|
Assignee: |
Fuji Xerox Co., Ltd.
|
Family ID: |
39329583 |
Appl. No.: |
11/810025 |
Filed: |
June 4, 2007 |
Current U.S.
Class: |
347/14 ;
347/10 |
Current CPC
Class: |
B41J 11/0095 20130101;
B41J 11/007 20130101; B41J 11/008 20130101; B41J 29/38
20130101 |
Class at
Publication: |
347/14 ;
347/10 |
International
Class: |
B41J 29/38 20060101
B41J029/38 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 31, 2006 |
JP |
2006-296170 |
Claims
1. A droplet ejecting apparatus comprising: a droplet ejecting head
for ejecting droplets onto a recording medium; a moving unit for
moving the recording medium relative to the droplet ejecting head;
an output unit for outputting a pulse signal which is generated
along with moving of the moving unit and which has a pulse width
comprising a cyclic fluctuation; a reference position detection
unit for detecting a reference position in the cyclic fluctuation;
a pattern memory for storing image information of a detection
pattern comprising a plurality of unit patterns which are set in
advance; a reading unit for reading an image formed on the
recording medium; a detection pattern output unit that drives the
droplet ejecting head based on the pulse signal outputted from the
output unit and the image information of the detection pattern
stored in the pattern memory when a detection pattern output
instruction is present; a correction information generating unit
that makes the reading unit read an image on the recording medium
on which the detection pattern image is formed by the detection
pattern output unit, derives a distance between the unit patterns
adjacent each other based on the image read by the reading unit,
compares the distance with a distance according to a conveyance
velocity of the recording medium by the moving unit, and generates
correction information so as to enlarge the pulse width when the
derived distance is shorter than the distance according to the
conveyance velocity, and to reduce the pulse width when the derived
distance is longer than the distance according to the conveyance
velocity; a memory that stores the correction information generated
by the correction information generating unit; a correction unit
for correcting the pulse width of the pulse signal outputted from
the output unit based on a detection timing of the reference
position by the reference position detection unit and the
correction information stored in the memory; and a head controller
for forming an image according to image information on the
recording medium by controlling the droplet ejecting timing of the
droplet ejection head using the pulse signal corrected by the
correction unit.
2. The droplet ejecting apparatus of claim 1, wherein the memory
stores the correction information for each unit of a predetermined
number of continuous pulses.
3. The droplet ejecting apparatus of claim 2, wherein: the image
information of the detection pattern comprises the plurality of the
unit patterns each comprising the predetermined number of
continuous pulses; and the correction information generating unit
generates the correction information with an identical pulse width
for every unit of the predetermined number of continuous
pulses.
4. The droplet ejecting apparatus of claim 1, wherein the pattern
memory stores image data of the unit pattern, a number of the unit
patterns, and a distance between the unit patterns as the image
information of the detection pattern.
5. The droplet ejecting apparatus of claim 1, wherein the detection
pattern comprises the unit patterns of a number obtained by
dividing an amount of a single cycle of the cyclic fluctuation by a
unit of the predetermined number of continuous pulses.
6. The droplet ejecting apparatus of claim 1, wherein the detection
pattern comprises a larger number of the unit patterns than a
number corresponding to an amount of a single cycle of the cyclic
fluctuation.
7. The droplet ejecting apparatus of claim 6, further comprising a
recording medium front end detection unit that is provided
downstream in the recording medium moving direction from the
droplet ejecting head and detects the front end of the recording
medium, wherein the detection pattern output unit starts image
formation of the detection pattern when the recording medium front
end detection unit detects the front end of the recording medium,
and drives the droplet ejecting head so as to form an image of a
reference signal pattern indicating that the reference position has
been detected at a timing when the reference position is detected
by the reference position detection unit during execution of the
image formation of the detection pattern.
8. The droplet ejecting apparatus of claim 6, wherein the
correction information generating unit generates the correction
information by averaging the correction information of images of a
plurality of the corresponding unit patterns of different
cycles.
9. The droplet ejecting apparatus of claim 1, wherein the detection
pattern output unit drives the droplet ejecting head so as to start
the image formation of the detection pattern at the detection
timing of the reference position by the reference position
detection unit.
10. The droplet ejecting apparatus of claim 1, wherein the
detection pattern output unit drives the droplet ejecting head so
as to form an image of a reference signal pattern indicating that
the reference position has been detected at a timing when the
reference position is detected by the reference position detection
unit during the execution of image formation of the detection
pattern.
11. The droplet ejecting apparatus of claim 1, wherein the image of
the unit pattern comprises a single pixel.
12. The droplet ejecting apparatus of claim 1, wherein the image of
the unit pattern comprises a plurality of pixels.
13. The droplet ejecting apparatus of claim 1, further comprising
an updating unit for updating the correction information stored in
the memory.
14. The droplet ejecting apparatus of claim 1, wherein the
recording medium is an intermediate transfer medium.
15. The droplet ejecting apparatus of claim 1, wherein: the moving
unit comprises a conveyance belt that is stretched around a drive
roll and a driven roll which are rotated so as to convey the
recording medium; and the reference position is provided on the
peripheral face of the drive roll.
16. The droplet ejecting apparatus of claim 1, wherein: the moving
unit comprises a conveyance belt for moving the recording medium;
the reference position is provided on the conveyance belt; and the
reference position detecting unit is provided at the downstream
side in the recording medium moving direction of the droplet
ejecting head so as to detect the reference position.
17. The droplet ejecting apparatus of claim 1, wherein the reading
unit comprises a line sensor provided at the downstream side in the
recording medium moving direction of the droplet ejecting head.
18. The droplet ejecting apparatus of claim 1, wherein the
conveyance velocity is a design value.
19. The droplet ejecting apparatus of claim 1, wherein: the moving
unit comprises a conveyance belt for moving the recording medium;
and the conveyance velocity is a surface velocity of the conveyance
belt.
20. A droplet ejecting apparatus comprising: an image forming unit
comprising: a droplet ejecting head for ejecting droplets onto a
recording medium; a moving unit for moving the recording medium
relative to the droplet ejecting head; an output unit for
outputting a pulse signal which is generated along with moving of
the moving unit and which has a pulse width comprising a cyclic
fluctuation; a reference position detection unit for detecting a
reference position in the cyclic fluctuation; a pattern memory for
storing detection pattern image information comprising a plurality
of unit patterns which are set in advance; a detection pattern
output unit that drives the droplet ejecting head based on the
pulse signal outputted from the output unit and the image
information of the detection pattern stored in the pattern memory
when a detection pattern output instruction is present; a memory
that stores correction information for correcting the pulse signal
outputted by the output unit; a correction unit for correcting the
pulse width of the pulse signal outputted from the output unit
based on a detection timing of the reference position by the
reference position detection unit and the correction information
stored in the memory; and a head controller for forming an image
according to image information on the recording medium by
controlling the droplet ejecting timing of the droplet ejection
head using the pulse signal corrected by the correction unit, and
an information processing unit comprising: a reading unit for
reading an image formed on the recording medium; a correction
information generating unit that, when the image read by the
reading unit is an image on the recording medium which the
detection pattern output unit has formed, derives a distance
between the unit patterns adjacent each other based on the image
read by the reading unit, compares the distance with a distance
according to the conveyance velocity of the recording medium by the
moving unit, and generates correction information so as to enlarge
the pulse width when the derived distance is shorter than the
distance according to the conveyance velocity, and to reduce the
pulse width when the derived distance is longer than the distance
according to the conveyance velocity; and a transmitting unit for
transmitting the correction information generated by the correction
information generating unit to the image forming apparatus.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based on and claims priority under 35
USC 119 from Japanese Patent Application No. 2006-296170 filed Oct.
31, 2006.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to a droplet ejecting
apparatus.
[0004] 2. Related Art
[0005] The droplet ejecting apparatus such as an ink jet printer
forms an image by driving a recording head according to image data
and ejecting ink droplets onto a recording medium from nozzles of
the recording head.
[0006] In some recording head adopting full width array (FWA)
technology in which plural nozzles are arranged on scanning lines
throughout the entire width of the recording medium, for example, a
cord wheel is attached on a rotation shaft of a drive roll for
conveying the recording medium and a signal obtained by reading a
mark on the cord wheel by an optical sensor is used for droplet
ejection timing control.
[0007] The drive roll contains eccentric error due to manufacturing
reason. The cord wheel also contains installation error and a print
error of the mark thereon.
[0008] For the reason, cyclic mismatch is generated between an
encoder signal for use in print clock and conveyance velocity of
the recording medium so that the ejection timing deviates, thereby
causing a deviation in a droplet shot position on a paper.
SUMMARY
[0009] In consideration of the above circumstances, the present
invention provides a droplet ejecting apparatus.
[0010] According to an aspect of the invention, there is provided a
droplet ejecting apparatus comprising: a droplet ejecting head for
ejecting droplets onto a recording medium; a moving unit for moving
the recording medium relative to the droplet ejecting head; an
output unit for outputting a pulse signal which is generated along
with moving of the moving unit and which has a pulse width
comprising a cyclic fluctuation; a reference position detection
unit for detecting a reference position in the cyclic fluctuation;
a pattern memory for storing image information of a detection
pattern comprising plural unit patterns which are set in advance; a
reading unit for reading an image formed on the recording medium; a
detection pattern output unit that drives the droplet ejecting head
based on the pulse signal outputted from the output unit and the
image information of the detection pattern stored in the pattern
memory when a detection pattern output instruction is present; a
correction information generating unit that makes the reading unit
read an image on the recording medium on which the detection
pattern image is formed by the detection pattern output unit,
derives a distance between the unit patterns adjacent each other
based on the image read by the reading unit, compares the distance
with a distance according to a conveyance velocity of the recording
medium by the moving unit; and generates correction information so
as to enlarge the pulse width when the derived distance is shorter
than the distance according to the conveyance velocity, and to
reduce the pulse width when the derived distance is longer than the
distance according to the conveyance velocity; a memory that stores
the correction information generated by the correction information
generating unit; a correction unit for correcting the pulse width
of the pulse signal outputted from the output unit based on a
detection timing of the reference position by the reference
position detection unit and the correction information stored in
the memory; and a head controller for forming an image according to
image information on the recording medium by controlling the
droplet ejecting timing of the droplet ejection head using the
pulse signal corrected by the correction unit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Exemplary embodiments of the present invention will be
described in detail based on the following figures, wherein:
[0012] FIG. 1 is a schematic view showing the structure of an image
forming apparatus according to a first exemplary embodiment;
[0013] FIG. 2 is a diagram showing the positional relation between
a recording head, maintenance device and conveyance belt at the
time of maintenance;
[0014] FIG. 3 is a schematic diagram showing the structure of
around the recording head according to the first exemplary
embodiment;
[0015] FIG. 4 is a control block diagram of this exemplary
embodiment;
[0016] FIG. 5 is a block diagram of correction processing of print
clock according to this exemplary embodiment;
[0017] FIG. 6 is a timing chart showing the relation between
conveyance timing of a recording paper, print clock and print
permission timing to each recording head;
[0018] FIG. 7 is an explanatory diagram of deviation detection
pattern and an derivation method of correction amount based on the
deviation detection pattern;
[0019] FIG. 8 is a graph showing an example of the deviation amount
derived from a deviation amount detection pattern;
[0020] FIG. 9 is a graph showing a correction value derived based
on the deviation amount shown in FIG. 8 and an actual correction
value;
[0021] FIG. 10 is a timing chart showing a reference position
detection signal, reading signal and correction print clock
outputted form the correction print clock generating section;
[0022] FIG. 11 is an explanatory diagram of other deviation
detection pattern and an derivation method of the correction amount
based on the deviation detection pattern;
[0023] FIG. 12 is a graph showing an example of correction value
deviation between the head and end of the correction table;
[0024] FIG. 13 is a schematic diagram showing the structure of an
image forming apparatus according to a second exemplary embodiment;
and
[0025] FIG. 14 is a schematic diagram showing the structure around
the recording head according to other exemplary embodiment.
DETAILED DESCRIPTION
[0026] Hereinafter, the exemplary embodiments of the present
invention will be described with reference to the accompanying
drawings.
First Exemplary Embodiment
[0027] FIG. 1 schematically shows the structure of the image
forming apparatus 10 according to the exemplary embodiment of the
invention. As shown in the FIG. 1, the image forming apparatus 10
includes a paper feed tray 20, an exit tray 22 and plural rollers
24.
[0028] Recording papers P are accommodated in the paper feed tray
20. When an image is formed, the recording papers P are picked up
one by one from the paper feed tray 20 by the rollers 24, and
conveyed along a predetermined conveyance passage F within the
image forming apparatus 10 and ejected into the exit tray 22.
[0029] A conveyance belt 14 and a adherence unit 16 are disposed
along the conveyance passage F of this recording paper P. The
conveyance belt 14 is stretched around a drive roll 11 which
rotates in the direction of an arrow E and two driven rolls 12
which rotate following the rotation of the drive roll 11, and the
conveyance belt 14 rotates in the direction of an arrow G. The
adherence unit 16 presses the recording paper P conveyed on the
conveyance passage F against the conveyance belt 14 and applies
electric charge to the recording paper P so as to adhere the
recording paper P electrostatically to the conveyance belt 14.
[0030] A registration roller 26 is disposed on the upstream side of
the conveyance belt 14 of the conveyance passage F of the recording
paper P. The registration roll 26 carries out a paper skew
correction in order to prevent the recording paper P conveyed along
the conveyance passage F from being adhered in a state in which it
is skewed with respect to the conveyance direction.
[0031] A recording head array 18 constructed of four recording
heads 18Y, 18M, 18C, 18K which eject four color inks, yellow (Y),
magenta (M), cyan (C) and black (K) are provided at positions
opposing a recording face of the recording paper P adhered
electrostatically to the conveyance belt 14 in the conveyance
passage F of the recording paper P.
[0032] In each of the recording heads 18Y, 18M, 18C, 18K for the
respective colors, a head unit having plural ejection nozzles is
arranged over the entire width of the conveyance belt 14. This
structure is of full width array (FWA) type, constituted of plural
ejection nozzles.
[0033] While a member provided for each color is expressed with an
alphabet (Y/M/C/K) indicating each color, at the end of the
reference numeral, this alphabet at the end of the reference
numeral is omitted if description is made without distinguishing
colors.
[0034] As shown in FIG. 1, the image forming apparatus 10 of this
exemplary embodiment includes front/rear face inversion conveyance
passages R. When performing double-side printing, the recording
paper P is conveyed along the conveyance passage R after an image
is formed on one side when the recording paper face is inverted
such that the opposite face to the face in which the image is
formed opposes the respective recording heads 18Y, 18M, 18C,
18K.
[0035] Ink tanks 19 which stores inks of the respective colors are
provided between the conveyance belt 14 and the exit tray 22. Ink
from the ink tank 19 is supplied to the recording heads 18Y, 18M,
18C, 18K through an ink supply pipe (not shown).
[0036] Here, the recording heads 18Y, 18M, 18C, 18K are constructed
to be movable apart from the conveyance belt 14 by a drive
mechanism (not shown).
[0037] Maintenance devices 28A, 28B are provided on the upstream
side and downstream side in the conveyance passage F of the
recording heads 18Y, 18M, 18C, 18K. The maintenance device 28A
includes maintenance units 30K, 30C for black and cyan and the
maintenance device 28B includes maintenance units 30M, 30Y for
magenta and yellow. The respective maintenance devices 28A, 28B are
constructed to be movable in a direction in which both of them
approach each other by a drive mechanism (not shown).
[0038] As shown in FIG. 2, the recording heads 18Y, 18M, 18C, 18K
are moved apart from the conveyance belt 14 at the time of
maintenance. Further, the maintenance devices 28A, 28B are moved
into a space between the recording heads 18Y, 18M, 18C, 18K and the
conveyance belt 14 generated by moving the recording heads 18Y,
18M, 18C, 18K.
[0039] Consequently, the maintenance units 30Y, 30M, 30C, 30K of
the maintenance devices 28A, 28B are disposed to oppose the four
recording heads 18Y, 18M, 18C, 18K and then maintenance processing
is executed appropriately by the respective maintenance units
30.
[0040] Maintenance processing to be executed by the maintenance
unit 30 includes sucking of ink liquid in the nozzle, wiping of ink
droplet adhering to the ejecting port of a nozzle, supply of ink
liquid into the nozzle and the like.
[0041] As shown in FIGS. 1, 2, a line sensor 25 is disposed in the
downstream of the recording head 18 in the conveyance passage F so
that an image printed on the recording paper P may be read.
[0042] As shown in FIG. 3, a disc-shaped encoder film 64 which
rotates with the drive roll 11 is attached to the rotation shaft of
the drive roll 11. Print timing marks 62 are provided radiantly
around the rotation shaft of the drive roll 11 on the peripheral
portion of the encoder film 64.
[0043] An encoder sensor 66 is provided at a position on this
peripheral portion so as to oppose the print timing marks 62. The
print timing mark 62 passing a reading position is read by the
encoder sensor 66. With a rotation of the drive roll 11, the print
timing marks 62 of the encoder film 64 pass the reading position of
the encoder sensor 66 successively.
[0044] The radiant print timing marks 62 are provided at an equal
interval on design and the print timing marks 62 are read at a
predetermined cycle when the drive roll 11 rotates at an equal
velocity. The detection cycle of the print timing marks 62 is
changed according to the rotation velocity of the drive roll
11.
[0045] As shown in FIG. 3, a reference position detection sensor 38
is provided in the vicinity of the drive roll 11. The reference
position detection sensor 38 detects a reference position mark
provided on the surface of the drive roll 11. The reference
position mark is provided at a position of the drive roll 11 and is
detected by the reference position detection sensor 38 each time
when the drive roll 11 turns a single turn. The reference position
detection sensor 38 outputs a detection signal which turns to high
when the reference position mark is detected.
[0046] As shown in the FIG. 3, a paper front end detection sensor
36 for detecting the front end of the paper P adhered on the
conveyance belt 14 is disposed on the upstream side in the
conveyance direction of the recording paper P with respect to the
recording head array 18. The paper front end detection sensor 36
detects presence or absence of any paper at a detection position
and outputs a paper front end detection signal which is high when a
paper is present and low when no paper is present. Therefore, rise
timing of the paper front end detection signal indicates the
detection timing of the front end of the recording paper P.
[0047] FIG. 4 is a block diagram showing the structure of the
control system of the image forming apparatus 10 of this exemplary
embodiment. As shown in FIG. 4, the image forming apparatus 10
includes a CPU 40 for controlling the entire system, ROM 42, RAM
44, interface (I/F) and the like and these components are connected
to a bus 48.
[0048] The image forming apparatus 10 is connected to an upper
level unit such as a computer through an I/F 46 and performs
printing based on image data and the like sent from the upper level
unit.
[0049] An I/O controller 61, a correction print clock generating
section 70, and a recording head controller 80 are connected to the
bus 48. The CPU 40 controls the I/O controller 61 and the recording
head controller 80 to control printing on the recording paper
P.
[0050] A maintenance drive circuit 50, a conveyance system drive
circuit 54 and a belt drive circuit 58 are connected to the I/O
controller 61.
[0051] A maintenance motor 52 for driving the maintenance unit 30
is connected to the maintenance drive circuit 50. When the
maintenance drive circuit 50 drives the maintenance motor 52, the
maintenance unit 30 cleans the recording head 18. That is, the I/O
controller 61 drives each drive circuit according to an instruction
of the CPU 40 so as to convey the recording paper P and clean the
recording head 18.
[0052] A conveyance system motor 56 for driving each roller of
passages F, R is connected to the conveyance system drive circuit
54. The conveyance system drive circuit 54 drives the conveyance
system motor 56 so as to convey the recording paper P within the
apparatus.
[0053] A belt conveying motor 60 for driving the drive roller 11 is
connected to the belt drive roller 58. The belt drive circuit 58
drives the belt conveying motor 60 to rotate the conveyance belt 14
in order to convey the recording paper P.
[0054] The paper front end detection sensor 36, the reference
position detection sensor 38 and the encoder sensor 66 are
connected to the I/O controller 61 and a detection result of each
sensor is inputted thereto so that printing is controlled by the
CPU 40 based on a detection result of each sensor.
[0055] The correction print clock generating section 70 is
connected to the recording head controller 80. The correction print
clock generating section 70 corrects a clock signal based on a
reading signal of the print timing mark 62 by the encoder sensor 66
based on correction information set preliminarily and outputs the
obtained correction print clock to the recording head controller
80.
[0056] The recording head controller 80 is connected to the
recording head 18 of each color through the head drive circuit 90.
The recording head controller 80 inputs an ink droplet ejection
signal based on image data into the head drive circuit 90 at a
timing according to the correction print clock signal generated by
the correction print clock generating section 70 so as to execute
ink droplet ejection control by the recording head 18.
[0057] That is, an ink droplet is ejected synchronously with the
correction print clock from the ejection nozzle of the recording
head 18 so that 1-dot ink droplet is ejected per a print clock.
[0058] The CPU 40 turns ON an ejection enable signal of each of the
recording heads 18Y, 18M, 18C, 18K to be inputted to the recording
head controller 80 at a timing based on a detection signal of the
paper front end detection sensor 36.
[0059] FIG. 5 shows the structure of the correction print clock
generating section 70 of this exemplary embodiment. As shown in
FIG. 5, the correction print clock generating section 70 includes a
correction table storage section 72, a correction processing
section 74, and a reference clock supply section 76.
[0060] A reading signal of the print timing mark 62 by the encoder
66 and a reference position detection signal from the reference
position sensor 38 are inputted to the correction print clock
generating section 70. The correction print clock generating
section 70 executes correction processing according to correction
information stored in the correction table storage section 72 with
the reference clock inputted from the reference clock supply
section 76 used as an operating clock.
[0061] The CPU 40 executes creation processing of the correction
information to the correction table storage section 72. In this
case, the CPU 40 executes reading of image data based on
information relating to deviation detection pattern A stored in the
ROM 42 or the like, print of the deviation detection pattern A via
the recording head controller 80, reading of an image on the
recording paper P by the line sensor 25 and creation of the
correction table based on image data outputted from the line sensor
25.
[0062] At this time, the CPU 40 inhibits correction of print clock
by the correction print clock generating section 70. Consequently,
the head drive circuit 90 is controlled based on a non-corrected
print clock in the recording head controller 80.
[0063] Hereinafter the operation of this exemplary embodiment will
be described.
[0064] When an upper level unit such as computer sends print data
and requests print, the CPU 40 outputs the print data sent with the
print request to the recording head controller 80 and controls the
conveyance system drive circuit 54 through the I/O controller 61 to
drive the conveyance system motor 56. Consequently, the recording
paper P is conveyed from the paper tray 20 to the conveyance belt
14 through the conveyance passage F.
[0065] When the recording paper P is conveyed onto the conveyance
belt 14, the front end of the recording paper P is detected by the
paper front end detection sensor 36. Then, when a detection result
is inputted to the CPU 40 through the I/O controller 61, the CPU 40
controls the head drive circuit 90 through the recording head
controller 80 to control printing of the recording head 18.
[0066] As shown in FIG. 6, ejection enable signals are turned ON
successively at a timing in which the recording paper P detected by
the paper front end detection sensor 36 reaches a recording
position (drop position of ink ejected from the recording head 18)
of each of the recording heads 18Y, 18M, 18C, 18K. Consequently,
images of respective colors are superimposed on the recording paper
P so as to form a color image.
[0067] Durations B to E from a timing A in which the front end of
the recording paper P is detected up to a timing in which an
ejection enable signal of each of the recording heads 18Y, 18M,
18C, 18K is turned ON are determined depending on a distance
between a detection position of the paper front end detection
sensor 36 and a recording position of each of the recording heads
18Y, 18M, 18C, 18K and conveyance velocity.
[0068] The distance between the detection position of the paper
front end detection sensor 36 and the recording position of each
recording head 18 may be determined with a design value or may be
corrected appropriately considering manufacturing tolerance at the
time of shipment from plant.
[0069] Then, the recording paper P which is printed by the
recording head 18 is conveyed along the conveyance passage F and
ejected to the exit tray 22.
[0070] The correction processing of the print clock used as a
control timing signal for the head drive circuit 90 in the
recording head controller 80 will be described.
[0071] The reading signal of the print timing mark 62 by the
encoder sensor 66 and the reference position detection signal from
the reference position sensor 38 are inputted to the correction
print clock generating section 70. The correction print clock
generating section 70 corrects this reading signal according to the
correction information stored in the correction table storage
section 72.
[0072] More specifically, a correction table as shown in Table 1,
for example, is set preliminarily and stored in the correction
table storage section 72. As shown in Table 1, the correction table
is set for steps in the unit of plural clocks.
[0073] According to this exemplary embodiment, the circumferential
length of the drive roll 11 is 110 mm and assuming that 5200 print
clocks are outputted per a single rotation of the drive roll, the
correction values are set for 50 steps (n=50). That is, 5200 clocks
on a single rotation are divided to 50 steps, 104 clocks for each
step.
TABLE-US-00001 TABLE 1 Correction Table Step No. Correction Value q
(nsec) 0 50 1 50 2 50 3 50 4 50 5 75 6 75 7 75 8 75 9 50 10 50 11
50 12 50 13 50 14 50 15 25 16 25 17 25 18 0 19 0 . . . . . . 49
50
[0074] In this exemplary embodiment, while correction of reading
signal by the correction print clock generating section 70 is
inhibited by the CPU 40, a deviation detection pattern A is printed
for each predetermined print clock by the recording head 18. The
printed deviation detection pattern A is read by the line sensor 25
and then, an interval T between the deviation detection patterns A
printed at adjacent positions and a design value S of the interval
of the adjacent deviation detection patterns A according to the
specification of the image forming apparatus 10 are compared based
on the obtained image data so as to correct the print clock
according to the deviation amount Z.
[0075] FIG. 7 shows an example in a state in which the deviation
detection pattern A is printed on the recording paper P at each
predetermined print clock. In the example indicated in FIG. 7, the
deviation detection pattern A is an ink droplet of a dot and the
deviation detection pattern A is printed every 104 dots (equal to a
step).
[0076] That is, the CPU 40 inputs image data based on information
concerning the deviation detection pattern A stored in the ROM 42
preliminarily into the recording head controller 80. Further, the
CPU 40 starts printing of the deviation detection pattern A at a
timing in which the reference position detection signal outputted
from the reference position detection sensor 38 turns to HIGH. At
this time, correction of the print clock by the correction print
clock generating section 70 is inhibited. Consequently, the head
drive circuit 90 is controlled by the recording head controller 80
based on a non-corrected print clock.
[0077] When start of printing is instructed by the CPU 40, the
recording head controller 80 controls the head drive circuit 90 so
as to print the deviation detection pattern A every 104 clocks.
[0078] The line sensor 25 reads the deviation detection patterns A
printed on the recording paper P by the recording head 18
successively and outputs them as image data.
[0079] The CPU 40 stores image data outputted from the line sensor
25 in the RAM 44 temporarily and specifies position information
(a.sub.k, b.sub.k), (a.sub.k+1, b.sub.k+1) of print start positions
of adjacent deviation detection patterns A.sub.k, A.sub.k+1 based
on the stored image data.
[0080] As indicated in FIG. 7, coordinate information of a case
where a position indicated by a point O in the Figure is home
position is used as position information.
[0081] The CPU 40 derives an interval T.sub.k of a print start
position according to an equation (1) based on specified position
information.
T.sub.k= {square root over
((a.sub.k+1-a.sub.k).sup.2+(b.sub.k+1-b.sub.k).sup.2)}{square root
over ((a.sub.k+1-a.sub.k).sup.2+(b.sub.k+1-b.sub.k).sup.2)} (1)
[0082] When the deviation detection pattern A is printed every 104
dots at a resolution of 1200 dpi, the design value S of the
interval between the adjacent deviation detection patterns A is
expressed in an equation (2).
S = 104 .times. 25.4 1200 = 2.201 ( 2 ) ##EQU00001##
[0083] Thus, a deviation amount Z.sub.k is expressed by a following
equation (3) using an interval T.sub.k of the printed deviation
detection patterns A and the design value S.
Z.sub.k=T.sub.k-S (3)
[0084] A correction time Q.sub.k may be derived by a following
equation (4) based on the deviation amount Z.sub.k and paper
conveyance velocity V (according to the example indicated in Table
2, it is assumed that the drive frequency of the head is 24 kHz and
the paper conveyance velocity is 508 mm/sec).
Q k = Z k / 104 V ( 4 ) ##EQU00002##
[0085] Following Table 2 shows the deviation amount Z of each step
derived using the above equations (1) to (4), the deviation amount
per dot of each step, a correction amount Q and a table value q set
on the correction table.
[0086] The deviation amount per dot may be obtained by dividing the
deviation amount Z by the quantity of clocks (104) contained in a
step. If the deviation amount Z is a minus value, the print clock
needs to be corrected by an amount of an absolute value of the
deviation amount Z in a plus direction. If the deviation amount Z
is a plus value, the print clock needs to be corrected by an amount
of an absolute value of the deviation amount Z in a minus
direction. Thus, Table 2 shows values obtained by multiplying the
deviation amount per dot with -1.
[0087] The table value q to be set on the correction table actually
is set step by step according to the resolution of the correction
processing section 74. Thus, the resolution of the correction
processing section 74 is a minimum resolution of the reference
clock supply section 76.
[0088] Table 2 indicates values of a case of correcting the print
clock in the unit of 25 nsec as the table value q with the
operating clock supplied from the reference clock supply section 76
as 40 MHz and the resolution of the correction processing section
74 as 25 nsec.
TABLE-US-00002 TABLE 2 Relation between deviation amount,
correction time and table value of each step Deviation Deviation
Correction amount amount per amount Actual correction Step No. Z
(.mu.m) dot (mm/dot) Q (n sec) value q (n sec) 0 -3.10 0.0000298 59
50 1 -3.10 0.0000298 59 50 2 -3.20 0.0000308 61 50 3 -3.20
0.0000308 61 50 4 -3.30 0.0000317 62 50 5 -3.40 0.0000327 64 75 6
-3.45 0.0000332 65 75 7 -3.50 0.0000337 66 75 8 -3.40 0.0000327 64
75 9 -3.25 0.0000313 62 50 10 -3.10 0.0000298 59 50 11 -2.90
0.0000279 55 50 12 -2.63 0.0000253 50 50 13 -2.35 0.0000226 45 50
14 -2.01 0.0000193 38 50 15 -1.61 0.0000155 31 25 16 -1.16
0.0000112 22 25 17 -0.67 0.0000064 13 25 18 -0.14 0.0000014 3 0 19
0.41 -0.0000039 -8 0 . . . . . . . . . . . . . . . 49 . . . . . . .
. . . . .
[0089] The deviation detection pattern A may be a dot as indicated
in FIG. 7 from the viewpoint of correction of the print clock.
However, if there is an omission of reading of the line sensor 25,
no accurate correction table may be obtained. Thus, actually, the
deviation detection pattern may be composed of plural dots
considering the reading accuracy of the line sensor. In case where
the deviation detection pattern A is composed of plural dots, the
omission of reading may be prevented by the plural dot structure
even if the reading accuracy of the line sensor is low. As a
result, an accurate correction table may be obtained.
[0090] FIG. 8 shows the deviation amount Z when the drive roll 11
is rotated by a single turn from the reference position detection
timing. As indicated in FIG. 8, the deviation amount fluctuations
while the drive roll 11 makes a single turn. This fluctuation is
estimated to result from eccentricity of the rotation shaft of the
drive roll 11 or the encoder film 64 attached to the rotation shaft
or an error in the arrangement interval of the print timing marks
62.
[0091] As shown in FIG. 8, the average of the deviation amount Z of
a single turn of the drive roll 11 never turns to 0. This is
because it that the deviation amount Z at a detection timing of the
reference position of the drive roll 11 is not 0.
[0092] FIG. 9 indicates the correction value Q and table value q
derived based on the deviation amount shown in FIG. 8. As indicated
in FIG. 9, the table value q is obtained by approximating the
derived correction value Q to values of every 25 nsec according to
the resolution of the correction processing section 74. The curve
of the table value q is almost inverse to the curve of the
deviation amount Z.
[0093] As shown in FIG. 10, the correction processing section 74
corrects the pulse width of an inputted reading signal only by the
correction value q stored in the correction table storage section
72. At this time, as the pulse width of a clock contained in the
same step, the same correction value q is used.
[0094] FIG. 10 indicates the correction value q of step 0 as q0 and
the correction value q of step 1 as q1. Because referring to Table
1, the correction value q of step 0 is 50 nsec, an amount for 104
clocks contained in the step 0 is outputted as the correction print
clock by adding 50 nsec to its pulse width.
[0095] In the example shown in FIG. 10, the correction processing
section 74 outputs the correction print clock by delaying it by an
amount for two clocks from the reading signal.
[0096] Although in the first exemplary embodiment, an example that
the delay period by the correction processing section 74 is an
amount for about two clocks in terms of the print clock has been
described, the delay period may be set appropriately considering
fluctuations in the maximum velocity.
[0097] In the first exemplary embodiment, an example that the
interval T is derived using the equation (1) has been described. In
the first exemplary embodiment, the deviation detection pattern on
the recording paper P kept adhered electrostatically onto the
conveyance belt 14 is read by the line sensor 25 disposed in the
downstream with respect to an ejection position of ink droplet of
the recording head 18 and therefore, coordinates in the nozzle
arrangement direction may be regarded as equal. Then, the interval
may be derived using a following equation (5).
T.sub.k=a.sub.k+1-a.sub.k (5)
(First Modification)
[0098] In the first exemplary embodiment, the example of starting
printing of the deviation detection pattern A based on a timing
when the reference position is detected after a paper front end is
detected in the creation processing of the correction table has
been described. Hereinafter, as a first modification, an example of
starting printing of the deviation detection pattern A based on a
timing when the paper front end is detected will be described.
[0099] The deviation detection pattern A printed at the head of the
recording paper P is not limited to A.sub.0 as shown in FIG. 11.
Thus, in the first modification, the detection mark R is printed at
a timing when the reference position is detected. As shown in FIG.
11, the detection mark R is printed in an area different from the
print area from the deviation detection pattern A.
[0100] The CPU 40 specifies the printed deviation detection pattern
A whose recording paper conveyance direction position is the same
as the detection mark R as A.sub.0 and creates a correction
table.
[0101] In this case, n+1 (51 in the example indicated in Table 1
and Table 2) or more deviation detection patterns A may be printed
or the deviation detection patterns A in an amount larger than the
number corresponding to a single turn may be printed.
(Second Modification)
[0102] If the deviation detection patterns A in an amount larger
than the number corresponding to a single turn are printed, plural
correction values Q are obtained in each step. Therefore, an actual
correction value q may be derived based on the plural correction
values Q.
[0103] At cycle joint portion indicated with a dotted line frame in
FIG. 12, there is a tendency that a large difference exists. To
reduce this difference to smoothen the joint, averaging procedure
may be performed.
[0104] At this time, the plural correction values Q may be averaged
simply as they are or may be averaged after weighting.
(Third Modification)
[0105] In the first exemplary embodiment, the example that the
design value is used as the conveyance velocity V of the recording
paper P has been described. An actually measured value of the
conveyance velocity may be used instead of the design value.
[0106] In this case, a mechanism for measuring the conveyance
velocity is needed.
[0107] For example, a Doppler measuring device capable of measuring
the surface velocity of the conveyance belt 14 may be used.
[0108] The Doppler measuring device calculates the velocity of an
object by measuring reflection waves of electromagnetic waves using
a fact that the frequencies of the reflection waves are changed by
Doppler effect when the object is moving in the advance direction
of the electromagnetic waves.
[0109] Although this Doppler measuring device may be provided on
the image forming apparatus 10, it only needs to be set when the
correction table is created, for example, at the time of shipment
from plant, and it does not need to be always equipped on the image
forming apparatus 10.
(Fourth Modification)
[0110] In the first modification, the example of creating the
correction table by reading the detection pattern A by the line
sensor 25 provided within the image forming apparatus 10 has been
described. Instead of this, may be configured so as to create the
correction table by scanning a recording paper P ejected to the
exit tray 22 after the detection pattern A is printed, by an
external device.
[0111] In this case, the external device obtains derivation of the
correction value based on the image data obtained by scanning and
create the correction table.
[0112] When correction table data indicating the created correction
table is inputted to the image forming apparatus 10, and stored in
the correction table storage section 72 by the CPU 40.
[0113] Because there sometimes occurs a difference in angle of an
original document between print time and scanning time, the
above-mentioned equation (1) may be used to derive the interval T
of the adjacent deviation detection patterns A.
Second Exemplary Embodiment
[0114] In the first exemplary embodiment, the image forming
apparatus 10 which executes the print directly on the recording
paper P has been described. As the second exemplary embodiment, an
image forming apparatus 200 in which an image is formed on an
intermediate transfer medium and then, the image formed on the
intermediate transfer medium is transferred to the recording paper
P will be described.
[0115] FIG. 13 shows the configuration of the image forming
apparatus 200 of the second exemplary embodiment. In FIG. 13, like
reference numerals are attached to the same components as the first
exemplary embodiment and description thereof are omitted.
[0116] As shown in FIG. 13, the image forming apparatus 200 of the
second exemplary embodiment ejects ink droplets to the intermediate
transfer medium 140 by the recording head 18. The intermediate
transfer belt 140 is stretched around a drive roll 130 and a driven
roll 132 and rotates in a direction of G.
[0117] The intermediate transfer belt 140 is flattened by the drive
roll 130 and one of the driven rolls 132 at a position opposing the
recording head 18.
[0118] A transfer roll 134 and a separation pawl 136 are disposed
in a rotation direction of the intermediate transfer belt 140 in
the downstream with respect to an ink droplet ejection position of
the recording head 18. The transfer roll 134 is pressed against the
driven roll 132 via the intermediate transfer belt 140 and
transfers an ink image from the intermediate transfer belt 140 to
the recording paper P when the recording paper P is conveyed while
pressed against the intermediate transfer belt 140. The separation
pawl 136 separates the recording paper P from the intermediate
transfer belt 140.
[0119] As shown in FIG. 13, a cleaning blade 138 is provided at a
position opposing the driven roll 132 in the downstream in the belt
rotation direction with respect to the separation pawl 136 and in
the upstream in the belt rotation direction of the recording head
18. The cleaning blade 138 wipes out ink left on the intermediate
transfer belt 140 without being transferred to the recording paper
P.
[0120] In the image forming apparatus 200 having such a structure,
the deviation detection pattern A is formed on the intermediate
transfer belt 140 in order to create the correction table.
[0121] The deviation detection pattern A formed on the intermediate
transfer belt 140 may be read by a line sensor 144 provided in the
downstream with respect to the ink droplet ejection position and in
the upstream with respect to the transfer position in the rotation
direction of the intermediate transfer belt 140. In this case,
transfer to the recording paper P is not needed.
[0122] In the meantime, the second modification may be modified
like from the first modification to the fourth modification.
[0123] Although in each of the above mentioned exemplary
embodiments, the example that the print timing mark 62 provided on
the encoder film 64 attached to the rotation shaft of the drive
roll 11 is read and used as the print clock has been described, the
invention is not limited to this example.
[0124] For example, the invention may be applied to an apparatus in
which the print timing mark 32 is attached to the conveyance belt
14 as shown in FIG. 14. As shown in FIG. 14, the print timing mark
32 is attached at a location not hidden by the recording paper P on
a face opposing the recording head array 18 of the conveyance belt
14 even in a condition in which the recording paper P is conveyed
in an adhered state. The print timing marks 32 are attached at an
equal interval in the conveyance direction along the entire
circumference of the conveyance belt 14. The interval of the print
timing mark 32 is an interval according to resolution in the
conveyance direction of the image forming apparatus 10.
[0125] As shown in FIG. 14, the encoder sensor 34 capable of
detecting the aforementioned timing mark 32 is disposed in the
upstream side in the conveyance direction of the recording paper P
with respect to the recording head array 18. Consequently, the
print timing marks 32 are detected successively by the encoder
sensor 34 with a rotation of the conveyance belt 14 by the drive
roll 11.
[0126] A conveyance belt reference mark 31 is provided at a
location on a face opposing the recording head array 18 of the
conveyance belt 14. A conveyance belt reference mark detecting
sensor 33 capable of reading the conveyance belt reference mark 31
is disposed in the downstream side in the conveyance direction of
the recording paper P of the recording head array 18.
[0127] In the conveyance belt reference mark detecting sensor 33,
the conveyance belt reference mark 31 is detected every time when
the conveyance belt 14 makes a single turn with a rotation of the
conveyance belt 14 by the drive roll 11.
[0128] Although FIG. 14 indicates an apparatus which ejects ink
droplets directly to the recording paper P, in description of the
image forming apparatus 200 mentioned in the second exemplary
embodiment, the conveyance belt 14 may replaced with the
intermediate transfer belt 140.
[0129] Although this exemplary embodiment has been described under
a condition in which the correction table is created at the time of
shipment from plant, the invention is not limited to this example,
but the correction table may be updated periodically. As the update
timing of this correction table, maintenance completion time, every
time when a predetermined quantity (for example, 10,000 pieces) is
recorded, an initialization time and the like may be mentioned.
[0130] Although in each of the above described exemplary
embodiments, the example that the deviation detection pattern A is
constituted of 1-dot ink droplet has been described, the invention
is not limited to this but the deviation detection pattern may be
constituted of plural dots. Further, it may be constituted in a
circular form or linear form of plural dots.
[0131] Although in the above-described exemplary embodiment, the
example that the deviation detection patterns are formed every 104
dots and the correction information is set in the unit of 104 dots
has been described, the invention is not limited to this. If the
cyclic fluctuation is large, correction accuracy may be raised by
setting a range smaller than 104 dots to increase the quantity of
correction steps. If the cyclic fluctuation is small, a range
larger than 104 dots is set to reduce the quantity of the
correction steps thereby reducing the correction processing time
and memory capacity.
[0132] The structure (see FIGS. 1-5) of the image forming apparatus
10 of this exemplary embodiment is just an example and the
invention may be modified appropriately within a range not
departing from the spirit of the invention.
[0133] The processing flow of the exemplary embodiment (see FIG.
10) is just an example also and needless to say, this may be
modified appropriately within a range not departing from the spirit
of the invention.
[0134] Although in this exemplary embodiment, the invention has
been described by taking an ink jet image forming apparatus as an
example, the invention may be applied to not only the ink jet image
forming apparatus but generally the droplet ejection apparatus for
a variety of industrial purposes, for example, production of a
color filter for the display which ejects colored ink onto polymer
film or formation of en EL display panel which ejects organic EL
solution onto a substrate.
[0135] The recording medium which is an object for image recording
in the droplet ejection apparatus of the invention widely includes
objects to which the droplet ejecting head ejects ink droplets.
Thus, although it is needless to say that the recording medium
includes the recording paper and OHP, it includes other recording
mediums, for example, polymer film.
[0136] The moving unit in the ink droplet ejection apparatus of the
invention includes widely any member which conveys the recording
medium, for example, the conveyance drum as well as the conveyance
belt of the above-described exemplary embodiment.
[0137] The foregoing description of the embodiments of the present
invention has been provided for the purpose of illustration and
description. It is not intended to be exhaustive or to limit the
invention to the precise forms disclosed. Obviously, many
modifications and variations will be apparent to practitioners
skilled in the art. The embodiments were chosen and described in
order to best explain the principles of the invention and its
practical applications, thereby enabling others skilled in the art
to are suited to the particular use contemplated. It is intended
that the scope of the invention be defined by the following claims
and their equivalents.
* * * * *